1. Field of the Invention
The present invention relates to a vehicular suspension that includes a trailing arm extending in the longitudinal direction of a vehicle body and a flexible arm extending in the vehicle width direction, wherein the outer end of the flexible arm is connected to the rear end of the trailing arm and flexes rearward when a wheel is braked, thereby making the wheel toe-in.
2. Description of the Related Art
FIG. 7 and FIG. 8 show a conventional vehicular suspension. A suspension 01 suspends a wheel W (right rear wheel) and includes a trailing arm 02, a lower arm 03, an upper arm 04, and a knuckle 05. The front end of the trailing arm 02 is pivotably supported on a vehicle body via a joint 06. The inner end of the lower arm 03 is pivotably supported on the vehicle body via a joint 07. The outer end of the lower arm 03 is welded to the rear end of the trailing arm 02. The outer end and the inner end of the upper arm 04 are pivotably supported via joints 08, 09 on the knuckle 05 and the vehicle body respectively.
The lower arm 03 is a substantially plate-like member with a bifurcated outer end including a first support portion 03a and a second support portion 03b. An expanded portion 03c is formed at the base parts of the first and second support portions 03a, 03b, and protrudes toward one side in the thickness direction of the lower arm 03. While the first and second support portions 03a, 03b of the lower arm 03 are in a state in which they are fitted around the outer periphery of a rear part of the trailing arm 02, the outer peripheral surface of the trailing arm 02 and the front surface of the lower arm 03 are welded by a weld w1, and the outer peripheral surface of the trailing arm 02 and the rear surface of the lower arm 03 are welded by a weld w2.
In this suspension 01, when a rearward load acts on the knuckle 05 when the wheel W is braked, the outer end of the lower arm 03 flexes rearward and at the same time the front end of the trailing arm 02 moves rearward and inward, thus making the wheel W toe-in to stabilizes the vehicle behavior during braking.
In this type of suspension 01, a large load acts on the welds w1 and w2 between the rear end of the trailing arm 02 and the outer end of the lower arm 03, causing a problem that the strength and the durability decrease. That is, the welds w1 and w2 receive not only a load accompanying vertical movement of the wheel W, but also a tensile load to peel off the weld w2 on the rear side in the case where a rearward load acts on the knuckle 05 when the wheel W is braked, and a tensile load to peel off the weld w1 on the front side in the case where a forward load acts on the knuckle 05 when the vehicle is accelerated. In particular, the load when braking is larger than that when accelerating.
Since the lower arm 03 is formed from a plate-like material, the lower arm 03 and the trailing arm 02 are in substantially line contact with each other, so that it is difficult to obtain a sufficient weld strength. In the above-mentioned conventional arrangement, the expanded portion 03c is formed on the base parts of the bifurcated first and second support portions 03a and 03b so as to improve the strength of the welds w1 and w2, but it is difficult to increase the strength and the durability of the welds w1 and w2 by the expanded portion 03c alone.
Furthermore, in the above-mentioned conventional arrangement, since the welds w1 and w2 are formed on the front side and the rear side respectively of the lower arm 03, it is necessary to change the attitude of the trailing arm 02 and the lower arm 03 during welding, thereby degrading the workability. Further, since the beads of the welds w1 and w2 have end parts, stress might be concentrated in the end parts, causing a problem that they easily become the starting point for a fracture. Moreover, since the bifurcated first and second support portions 03a and 03b are formed at the outer end of the lower arm 03, the vertical dimension of the lower arm 03 increases, causing a problem that the degrees of freedom are decreased in designing the suspension 01.